Impact Angle Dependence of Erosive Wear for Spheroidal Carbide Cast Iron
2017 Volume 58 Issue 7 Pages 1032-1037
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2017 Volume 58 Issue 7 Pages 1032-1037
Erosive wear (or erosion) is a phenomenon where the material surface is damaged and removed by the continuously impacting of particles. According to researches on erosion, three types of parameters affect erosion, namely, particle properties, impacting condition, and target material properties.
This study investigated the impact angle dependence of erosion by 3D Finite-Element-Method (FEM).
In the FEM analysis, the velocity of impact particles was set as 20 m/s and the analysis duration was 0.01 ms. The size of the target material was 10 × 10 × 10 mm. The parameters of the target materials were set same as spheroidal carbide cast iron (SCI) and spheroidal graphite cast iron (FCD). The impact particle was spherical shaped steel grits with a diameter of 700 μm. The impact angle was changed from 10 degree with a 10 degree interval, up to 90 degree. To verify the analytical results, single particle impact tests was conducted at the same time.
The results showed no difference in the equivalent plastic strain and Von Mises stress for spheroidal carbide cast iron with increasing impact angle, respectively. Both the equivalent plastic strain and Von Mises stress of FCD were largest around 60～80 degree. In addition, both the experimental and analytical results of the materials showed the same tendency. Therefore, by focusing on the plastic deformation of the material surface, it is possible to verify impact angle of dependence by 3D FEM analysis. The results of analysis indicate that spherical carbides can restrain the plastic deformation of the eroded surface.
This Paper was Originally Published in Japanese in J. JFS 88 (2016) 252–257.
The phenomenon that damage or loss from material surface by solid particles impact is called as erosive wear, or erosion, which has become an important problem for solid-fluid delivery or pneumatic conveying systems.
According to some previous researches, erosion were complicatedly influenced by many affecting factors, which can be classified into 3 categories, (i) particle properties such as hardness or particle shapes of impact particles (ii) impacting conditions such as impact velocity or impact angle, (iii) target material properties such as mechanical properties or microstructure of target material1–9). It is also reported that there are correspondent impact angle dependences for different kinds of iron and steel materials, the impact angle dependences usually vary according to hardness, particle diameters and shapes of impact10–13). In order to make it clear the impact dependence of ductile material, brittle material and spheroidal graphite cast iron, the erosion by repeated particles impact were simulated by means of single particle impact of 2D FEM models14,15). The results showed that the impact angle dependence of erosion can be reflected using the sum of equivalent plastic strain on the impacted surface10). However, the 2D FEM is too difficult to simulate impact particle with all kinds of shapes except axisymmetrical shapes, but 3D FEM has abilities to build impact particles with complex shapes so as to explain erosion mechanism through Von Mises stress verification. Moreover, 3D FEM also provides abilities to assign carbides in impacted material, which is helpful for further researches.
In this work, 3D single particle impact models for spheroidal carbide cast iron were built, the impact angle dependence of erosions were discussed from viewpoint of stress and equivalent plastic strain on the surface of impacted material.
The 3D single particle impact FEM models were established using LS-DYNA 971 (Livermore Software Technology Corporation, Livermore, CA, USA), which is suitable for contact problems. Simulations of single particle impact (1 particle in each impact) using spherical particle were conducted. The 3D FEM model is shown in Fig. 1. The velocity of impact particle was set as 20 m/s, equaling to the actual velocity of impact particles in erosion tests. Simulation duration was set as 0.01 ms, target material was built as 10 × 10 × 10 mm. Material parameters were set according to the mechanical properties of spheroidal carbide cast iron (SCI) and spheroidal graphite cast iron (FCD). In the simulation, diameters of spheroidal carbide (VC) and spheroidal graphite were set as 100 μm, they were assigned in a line in the target material with same adjacent interval. Sphere with diameter 700 μm were built as impact particle, impact angle were changed from 10 degree to 90 degree in increment of 10 degree. Because impact particles have no deformation approximately during erosion, the impact particle was set as rigid body, but target material is still set as elastic material. The material parameters of impact particle and target material are listed in Table 115,16).
| SCI | FCD | Impact particle | |||
|---|---|---|---|---|---|
| Target material | Carbide(VC) | Target material | Graphite | ||
| Mass density, kg/mm3 | 8.0 × 10−6 | 1.5 × 10−5 | 8.0 × 10−6 | 1.6 × 10−6 | 8.0 × 10−6 |
| Young’s modulus, GPa | 200 | 530 | 161 | 7 | 210 |
| Poission ratio | 0.30 | 0.22 | 0.25 | 0.10 | 0.3 |
| Yield stress, MPa | 500 | 6000 | 230 | 30 | — |
The tests of single particle impact were also conducted to verify the simulation results. The results of tests and simulation were compared by discussing the correlation of crater depth between analytical value and actual measurement value.
2.2 Tests of single particle impactThe objective of single particle impact tests is to verify analytical results mentioned in section 2.1. Blast machine was used to conduct tests. The schematic view of blast machine and photographs of impact particles in the tests are shown in Fig. 2. Compressor generates air pressure up to 5 kgf/cm2, forming air flow of 100 m/s, accelerating impact particles up to 20 m/s. Single particle impact tests were conducted under 3 impact angles of 30 degree, 60 degree and 90 degree. The indentation depth of craters under these 3 impact angles were measured using microscope (VHX-2000, KEYENCE, Japan). 10 different indentation depths of craters were measured and then the mean value of these indentation depths were calculated to be used. Spheroidal carbide cast iron (SCI) and spheroidal graphite cast iron (FCD) were used as specimens. Spherical steel grits with average diameter 700 and hardness 420 HV1 were used as impact particles. The chemical compositions of specimens were listed in Table 2, the photographs of microstructure of specimens were shown in Fig. 3.
3D model. (a) Appearance of 3D model, (b) Cross sectional view of 3D model.
Schematic view of blast machine and spherical shaped steel grits. (a) Blast machine, (b) Steel grits.
| (mass%) | |||||||
|---|---|---|---|---|---|---|---|
| C | Si | Mn | Mo | V | Fe | others | |
| FCD | 3.75 | 2.15 | 0.22 | — | — | Bal. | P, S |
| SCI | 2.79 | 0.96 | 0.54 | 3.06 | 12.7 | Bal. | P, S |
Microstructure of specimens. (a) FCD, (b) SCI.
The craters of single particle impact simulation under impact angle 30 degree are shown in Fig. 4. It is found that along the impact direction, tiny material piled up at the color change region from blue to red, which were in agreement with the phenomenon of tiny pile-up material on specimens due to rotation of impact particle at impact moment in tests. The analytical results under 3 impact angles of 30 degree, 60 degree and 90 degree are shown in Fig. 5. It is found that surface deformation occurred at all target materials, and it is also found that obvious deformation occurred on spheroidal graphite, but no deformation occurred on spheroidal carbide.
3D observation of indentation depth generate on the target surface for FEM model. (a) FCD, (b) SCI.
Results of 3D FEM analysis for single particle impact.
The indentation depth of craters from simulation under 3 impact angles of 30 degree, 60 degree and 90 degree were measured. The relationship between simulation time and the indentation depth at the deepest point on target material after simulation were shown in Fig. 6. In Fig. 6, horizontal axis is simulation time (From the moment that impact particle contacted with target material to the moment that impact particle entirely departed away from target material), vertical axis is indentation depth. It is found that indentation became deeper along the sequence of impact angle 30 degree, 60 degree and 90 degree. In addition, it is also found that deformation recovered a little at all impact angles.
Indentation depth as function of impact time for specimens. (a) FCD, (b) SCI.
The appearances of crater and indentation depth after single particle impact tests were observed and measured using microscope. The photographs of typical craters are shown in Fig. 7. It is found that tiny material piled up on specimens at impact angles 30 degree and 60 degree, which is in agreement with the analytical results. The indentation depth of spheroidal graphite cast iron became deeper with increasing of impact angle, they were 7.62 μm, 14.88 μ and 18.70 μm at impact angle 30 degree, 60 degree and 90 degree respectively. Similar tendency were also found on the indentation depth of spheroidal carbide cast iron, they are 3.00 μm, 10.38 μm and 15.48 μm at impact angle 30 degree, 60 degree and 90 degree respectively.
Observation of indentation of specimens in single particle impact tests. (a) FCD, (b) SCI.
The correlation diagram between indentation depths from simulation in section 3.1 and those from single particle impact tests in section 3.2 are shown in Fig. 8. The correlation coefficient of indentation depth between analytical results and test results on FCD and SCI were calculated, both are 0.99, close to 1, demonstrating strong correlation between analytical results and test results. Therefore, in the following section, impact angle dependence of erosion are explained from view point of equivalent plastic strain and stress from single particle impact simulation.
Correlation diagram of analytical value and actual measurement value. (a) FCD, (b) SCI.
According to shear strain energy theory when the shear strain energy in the actual case exceeds shear strain energy at the time of failure the material fails. Von mises stress is in proportion to the square root of shear strain energy. Von mises stress is expressed by a combination of three principal stress, so it can be used as an evaluation of mechanical state for iron and steel materials. The Von mises stress after simulation are shown in Fig. 9. It is found that, as for spheroidal graphite cast iron, obvious deformation occurred on spheroidal graphite, obvious von mises stress also occurred at thick places of target materials besides material surface, and von mises stress on spheroidal graphite were lower than those on matrix around spheroidal graphite. Meanwhile, as for spheroidal carbide cast iron, von mises stress on spheroidal carbide were higher than those on matrix around spheroidal carbide, which is because the yield stress of spheroidal carbide is very high, up to around 6000 MPa.
Von mises stress distribution of specimens by FEM analysis.
Erosion is a phenomena of material deformation and loss caused by repeated impact of solid particles, it can be seen as the results of deformation accumulation on material surface by single particle impact. So impact angle dependence of erosion can be explained through equivalent plastic strain on material surface. The cross sectional view of equivalent plastic strain distribution on spheroidal graphite cast iron and spheroidal carbide cast iron under impact angles of 30 degree, 60 degree and 90 degree are shown in Fig. 10. It is found that equivalent plastic strain distribution of 90 degree is axisymmetric, and equivalent plastic strain of 30 degree is obvious in a small region. In addition, it is also found that equivalent plastic strain on the spheroidal graphite were larger than those on matrix around spheroidal graphite, and equivalent plastic strain on the spheroidal carbide were smaller than those on matrix around spheroidal carbide. The ratio of total equivalent plastic strain on FCD and SCI (total equivalent plastic strain on FCD and SCI were divided by total equivalent plastic strain on FCD at impact angle 90 degree) under different impact angles are shown in Fig. 11, and relationship between erosion rate and impact angle are shown in Fig. 12. It is found that both equivalent plastic strain and erosion rate increased firstly and then decreased, maximum value occurs around a higher impact angle, showing a similar tendency. In addition, it is also found that equivalent plastic strain and erosion rate of SCI changed much less at different impact angles comparing to FCD, showing that the impact angle dependence is very small. But the tendencies of both SCI curves are different, which is because the arrangement of VC in specimens for tests are much more complex than those in target material for simulation. According to discussions above, equivalent plastic strain at different impact angles can be regarded as a method to explain the features of impact angle dependence that erosion of FCD increases firstly and then decreases with maximum value occurring at a higher impact angle, and erosion of SCI changes a little at different impact angles. In other word, impact angle dependence of erosion can be approximately discussed through equivalent plastic strain of single particle impact.
Equivalent plastic strain distribution of specimens by FEM analysis.
Total equivalent plastic strain as function of impact angle for specimens.
Erosion rate as function of impact angle for specimens.
The difference between impact angle of erosion for FCD and SCI is due to the influence of spheroidal graphite and spheroidal carbide in target material. Yield strength of spheroidal carbide is much higher than that of spheroidal graphite, up to 5500 MPa or higher. So it is inferred that the existence of spheroidal carbide with high yield strength in target material can largely restrain the impact angle dependence of erosion.
In this work, 3D FEM models were built, and the impact angle dependence of erosion on spheroidal carbide cast iron were verified using analytical results from view point of stress and equivalent plastic strain.
(1) As for spheroidal graphite cast iron, obvious deformation was found on the spheroidal graphite in target material. And von mises stress in matrix was higher than that on spheroidal graphite.
(2) As for spheroidal carbide cast iron, von mises stress on the spheroidal carbide was higher than that on the matrix around spheroidal carbide, but no deformation was found on the spheroidal carbide. The plastic deformation on spheroidal carbide cast iron was largely restrained because of the existence of spheroidal carbide with much higher yield stress comparing to spheroidal graphite in spheroidal graphite cast iron.
(3) There are similar curves for impact angle dependence of erosion and that of equivalent plastic strain, so impact angle dependence of erosion can be explained with that of equivalent plastic strain.
